Down-regulated in adenoma Cl/HCO3 exchanger couples with Na/H exchanger 3 for NaCl absorption in murine small intestine.
OBJECTIVE
Electroneutral NaCl absorption across small intestine contributes importantly to systemic fluid balance. Disturbances in this process occur in both obstructive and diarrheal diseases, eg, cystic fibrosis, secretory diarrhea. NaCl absorption involves coupling of Cl(-)/HCO(3)(-) exchanger(s) primarily with Na(+)/H(+) exchanger 3 (Nhe3) at the apical membrane of intestinal epithelia. Identity of the coupling Cl(-)/HCO(3)(-) exchanger(s) was investigated using mice with gene-targeted knockout (KO) of Cl(-)/HCO(3)(-) exchangers: Slc26a3, down-regulated in adenoma (Dra) or Slc26a6, putative anion transporter-1 (Pat-1).


METHODS
Intracellular pH (pH(i)) of intact jejunal villous epithelium was measured by ratiometric microfluoroscopy. Ussing chambers were used to measure transepithelial (22)Na(36)Cl flux across murine jejunum, a site of electroneutral NaCl absorption. Expression was estimated using immunofluorescence and quantitative polymerase chain reaction.


RESULTS
Basal pH(i) of DraKO epithelium, but not Pat-1KO epithelium, was alkaline, whereas pH(i) in the Nhe3KO was acidic relative to wild-type. Altered pH(i) was associated with robust Na(+)/H(+) and Cl(-)/HCO(3)(-) exchange activity in the DraKO and Nhe3KO villous epithelium, respectively. Contrary to genetic ablation, pharmacologic inhibition of Nhe3 in wild-type did not alter pH(i) but coordinately inhibited Dra. Flux studies revealed that Cl(-) absorption was essentially abolished (>80%) in the DraKO and little changed (<20%) in the Pat-1KO jejunum. Net Na(+) absorption was unaffected. Immunofluorescence demonstrated modest Dra expression in the jejunum relative to large intestine. Functional and expression studies did not indicate compensatory changes in relevant transporters.


CONCLUSIONS
These studies provide functional evidence that Dra is the major Cl(-)/HCO(3)(-) exchanger coupled with Nhe3 for electroneutral NaCl absorption across mammalian small intestine.
Walker
Nancy M
NM
Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri 65211-3300, USA.
Simpson
Janet E
JE
Yen
Pei-Fen
PF
Gill
Ravinder K
RK
Rigsby
Elizabeth V
EV
Brazill
Jennifer M
JM
Dudeja
Pradeep K
PK
Schweinfest
Clifford W
CW
Clarke
Lane L
LL
D000236:Adenoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D000818:Animals; D027963:Chloride-Bicarbonate Antiporters / Q000235:genetics* / Q000378:metabolism; D004195:Disease Models, Animal; D015536:Down-Regulation; D005455:Fluorescent Antibody Technique; D006863:Hydrogen-Ion Concentration; D007408:Intestinal Absorption / Q000502:physiology*; D007424:Intracellular Fluid / Q000378:metabolism; D017136:Ion Transport / Q000502:physiology; D007580:Jejunal Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D007583:Jejunum / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008817:Mice, Mutant Strains; D016133:Polymerase Chain Reaction; D012334:RNA, Neoplasm; D012965:Sodium Chloride / Q000378:metabolism*
D027963:Chloride-Bicarbonate Antiporters; D012334:RNA, Neoplasm; D012965:Sodium Chloride